Bounds on information exchange for byzantine agreement

Abstract

Byzantine Agreement has become increasingly important in establishing distributed properties when there may exist errors in the systems. Recent polynomial algorithms for reaching Byzantine Agreement provide us with feasible solutions for obtaining coordination and synchronization in distributed systems. In this paper we study the amount of information exchange necessary to ensure Byzantine Agreement. This is measured by the number of messages and the number of signatures appended to messages (in case of authenticated algorithms) the participating processors need to send, in the worse case, in order to reach Byzantine Agreement. The lower bound for the number of signatures in the authenticated case is ~(nt), where n is the number of participating processors and t is the upper bound on the number of faults. If n is large compared to t, it matches the upper bounds from previously known algorithms. The lower bound for the number of messages is Δ(n+t2). We present an algorithm that achieves this bound and for which the number of phases does not exceed the minimum t+1 by more than a constant factor.